1. Field of the Invention
The present invention relates generally to the field of light emitting devices. The present invention relates to a light emitting device that can be used, for example, as an indicator, a lighting apparatus, a display, or a backlight light source for liquid crystal display.
2. Description of Related Art
In recent years, various semiconductor devices have been proposed and put into practical use. Yet the demand for high performance is ever increasing. In particular, there is an increasing need for electrical components that can maintain performance for long periods of time even in severe environments. The same applies for light emitting diodes (LEDs) and other light emitting devices. Requirements for higher performance in the area of general lighting, in-vehicle lighting, and the like, is growing daily. Demand has increased for devices that can yield higher output (higher luminance) and higher reliability, while having a low cost.
Generally, a light emitting device includes a base member on which electric components such as a semiconductor light emitting element (hereinafter referred to as a light emitting element) and a protective element are mounted, and a conductive member for supplying electric power to these electric components. The light emitting device may further include a sealing member to protect the electric components from the external environment.
In such light emitting devices, various kinds of bonding members may be employed to mount the light emitting element on the base member. The bonding member may be made of a thermosetting resins such as an epoxy resin and a polyimide resin. The thermosetting resin may contain a filler such as Ag or silica. Furthermore, in order to meet the recent demands of higher output of the light emitting devices, Au—Sn and Sn—Ag—Cu based solder materials or materials made of a metal such as silver solder may be used to improve the heat dissipation properties and reliability of the devices, as described, for example, in JP 2005-191135A.
However, such bonding members described above which are employed in the light emitting devices have lower light reflectivity and higher optical absorptance compared to the materials which are typically used in a reflective member. Therefore, in the light emitting devices having a conventional structure, light is absorbed by the bonding member located near the light emitting element, which can causes problems due to insufficient light being provided by the light emitting device.
For example, a bonding member containing a resin may be deteriorated and/or discolored by light and heat generated from the light emitting element, which may result in an increase in the optical absorptance.
Even when a bonding member made of a metal which does not deteriorate is employed, the light reflectivity of the metal materials typically used in the bonding member is lower than that of the materials typically used in a reflective member.
Further, when a large amount of the bonding member applied to obtain reliable bonding spreads to the surroundings of the light emitting element, the optical loss is particularly large.
As described above, in the light emitting devices having a conventional structure, light may be absorbed by the bonding member located near the light emitting element, which causes a problem in which sufficient light can not be extracted.